1. Field of the Invention
The present invention relates generally to tape measures and, more particularly, to a tape measure with a self-regulating speed control mechanism by which when a blade that has been extracted from a casing is retracted into the casing, the retraction speed of the blade is self-controlled such that a predetermined speed is maintained.
2. Description of the Related Art
Generally, a tape measure includes a casing in which a bobbin is rotatably provided. One end of a blade (referred to simply as a “tape”) is wound around the bobbin, and the other end thereof protrudes out of the casing. The end of the blade that protrudes out of the casing is pulled and extracted and then used to make a variety of measurements.
To rewind the blade around the bobbin again after the measurements have been completed, a first elastic member is coupled to the bobbin and provides elastic rotating force to the bobbin. A plate spring which is wound up in a coil shape is typically used as the first elastic member.
When the blade is returned to its original position by the elastic force of the first elastic member, the speed at which the blade is retracted into the casing is gradually increased by the elastic force of the first elastic member. Therefore, if the portion of the blade that is extracted from the casing is very long, the acceleration of the blade which is being retracted into the casing is excessively increased. Thus, a user who is using the tape measure or nearby people may be injured or the tape measure itself may be damaged.
In an effort to overcome the above-mentioned problem, techniques incorporated herein were proposed in U.S. Pat. No. 3,889,897 (registered on Jun. 17, 1975), entitled “COILABLE TAPE MEASURING DEVICE HAVING A SELF-REGULATING SPEED CONTROL MECHANISM”, and in US Patent No. 2008-0263886, entitled “TAPE MEASURE WITH A SELF-REGULATED SPEED CONTROL MECHANISM”.